Abstract: Processes for upgrading a heavy oil or heavy oil-derived feedstock in presence of an ionic liquid are described, and can improve the heavy oil or heavy oil-derived properties such as viscosity and composition, and reduced contaminant content, such as a reduced Total Acid Number (TAN) and a reduced heavy metal content. Processes for upgrading heavy oil or heavy oil-derived in presence of an ionic liquid can include a catalytic cracking treatment carried out under catalytic cracking conditions, and/or a non-catalytic treatment, as well as various separation steps to separate the ionic liquid or a diluent if present in the feedstock. The ionic liquids that can be used in the context of the processes described herein include ionic liquids that are feed-miscible or feed-immiscible.